for in 用法

apple_wxs

/** * for in 循环，每次取的是obj对象 的 key 值。 */    //得到对象的keys集合//    in 左边的可以是表达式，function keys(obj){var ret = new Array();var i = 0;for (ret[i++] in obj);return ret;}//得到对象的values集合function values(obj){var ret = new Array();for (var i in obj){//alert("i = " + i);//i值为obj的keyret.push(obj[i]);}return ret;}var o = new Object();o.x = 1;o.y = 2;o.name = "test object";alert("all key:" + keys(o));alert("all value:" + values(o));//数组的情况var arr = ["a","b","c"];arr.name = "myArr";alert("all key:" + keys(arr));alert("all value:" + values(arr));//所以不建议用for in 方式操作数组。